docs: def _process_mark_toggle(self, p_todo_id, p_force=None):
          """
          Adds p_todo_id to marked_todos attribute and returns True if p_todo_id
          is not already marked. Removes p_todo_id from marked_todos and returns
          False otherwise.
  
          p_force parameter accepting 'mark' or 'unmark' values, if set, can force
          desired action without checking p_todo_id presence in marked_todos.
          """
          if p_force in ['mark', 'unmark']:
              action = p_force
          else:
              action = 'mark' if p_todo_id not in self.marked_todos else 'unmark'
  
          if action == 'mark':
              self.marked_todos.add(p_todo_id)
              return True
          else:
              self.marked_todos.remove(p_todo_id)
              return False